Siloxane modified polyolefin copolymers have been long known in the art and have various industrial applications. They retain the favorable characteristics of both polysiloxanes and polyolefins. Polysiloxanes are known for their thermostability, chemical stability, low surface energy, and lubricating properties. Poly-.alpha.-olefins are chemically stable, have high resistance against physical force, and molding or shaping capability. The .alpha.-olefin polymers are usually mixed with other hydrocarbon polymers such as polyethylene and polypropylene. Mixing siloxane polymers with .alpha.-olefin polymers leads to leaching; i.e., one polymer forms a layer or film on the other polymer.
Siloxane modified polyolefin copolymers were developed for use as electrical insulating material and as substitutes for polyethylene. The siloxane modified polyolefin copolymers are synthesized by reacting low molecular weight polyolefins with cyclosiloxanes in the presence of catalysts such as Ziegler-Natta catalysts, peroxides and other free radical initiators and at temperatures from 100.degree. to 200.degree. C. These copolymers were also made by melt mixing polyolefins and olefin substituted siloxanes. These products are both graft copolymers and block copolymers.
Another way of combining hydrocarbons and siloxanes is by reacting functional groups attached to each of the oligomers, macromers, polymers or monomers. Carboxylic acids or anhydrides can link with hydroxyl groups to form esters, primary and secondary amines to form amides or imides, primary amines to form imides and tertiary amines to form quaternary amine salts. The amides, imides and esters are more stable than the quaternary ammonium salts. As is to be expected, the ionic link of the quaternary salt hydrolyzes on standing. The chemical bonds found in the esters, imides and amides appear to be quite stable during use.
There have been problems producing chemically bonded siloxane and polyalkyl copolymers. If there is more than one functional group on the silicone oligomer, the product may be unacceptable. Subsequent processing into thin structures, e.g. extruding or co-extruding the material into films or sheets, becomes difficult.
It has now been found that by reacting functional derivatives of siloxanes with substantially one reactive group per molecule and polyolefins polymers containing one or more functional groups, copolymers containing the siloxane functionality and polyethylene or other polyalkyl functionality can be obtained. The oligomers are reacted at defined ratios and under specific temperature and mixing conditions in an extruder. Some difunctional or multifunctional groups can be present. The level of these difunctional or multifunctional groups determines the level of cross linking in the final product. Cross linking can cause problems when forming copolymers into thin films, sheets or bottles. Preferably, monofunctional silicone reactants are used. The copolymers obtained by this method can be mixed directly with other polymers or coextruded with other polymers into multilayer structures, including sheets, films or bottles.
Silicone containing copolymers have a tendency to migrate to the surface of films and plastics. The mixed copolymers made herein acquire surface characteristics of the silicone polymer, but have the advantage that the siloxane is chemically linked to another polymer. Thus the siloxane does not separate or leach out of the film or package as the physical mixtures can. The films and plastics obtained by this invention are particularly useful in packaging, for measuring and dispensing devices, and adhesive releasing materials. They are particularly useful for making bottles for low surface energy liquids.
It is an object of the present invention to provide copolymers which have the favorable characteristics of both polysiloxanes and polyolefins, but are thermoplastic, heat-sealable and more stable than mixtures of the polymers.
It is also an object of the present invention to provide a practical and efficient process to obtain a siloxane modified polyolefin. The process does not require a solvent and therefore is environmentally sound and more economical to run.
It is further an object of the present invention to provide a convenient method of using these siloxane modified polyolefins with other polymers to make films and other plastic articles.